Non-linear signalling device for vehicles

ABSTRACT

A light bar is provided for mounting to a roof of an emergency vehicle such that the signalling devices comprising the light bar are distributed across the roof to form a non-linear pattern. A dome assembly covers the signalling devices and also forms a non-linear pattern traversing the roof. The light bar provides for enhanced visibility at angles approaching 90° to the heading of the vehicle. Moreover, the non-linear pattern of the signalling devices allows the light bar to provide a signalling pattern whose warning effect can be alternatively directionalized into different distinct zones about the vehicle. In a preferred embodiment, each of the signalling devices is contained in a module comprising a base and a dome such that enhanced transmittance of light is provided at angles approaching 90° from the heading of the vehicle.

TECHNICAL FIELD

The invention is generally directed to signalling systems for emergencyvehicles and more particularly, is directed to warning light assembliesfor mounting to emergency vehicles.

BACKGROUND

Although warning light assemblies for emergency vehicles are used inmany types of situations, one of the most common uses is to provide aneffective warning for the vehicles as they approach trafficintersections. Despite the use of warning light assemblies in thissituation, often accompanied by the use of sirens, collisions atintersections remain a serious problem for emergency vehicles.

With the increasing popularity of air conditioning and stereo systems invehicles, sirens are often not heard. The sound of conditioned airthrough the ducting of a vehicle coupled with a loud stereo often meansthat an emergency vehicle is not identified until its warning lights arenoticed. As air conditioning and audio systems in vehicles proliferate,it is important to maximize the ability of warning lights for emergencyvehicles to warn other vehicles of their approach, particularly atintersections.

Traditionally, warning light assemblies for an emergency vehicle havebeen mounted on a base that traverses a roof of the vehicle. The warninglights are distributed substantially in a row across the roof and areenclosed by one or more transparent domes that protect the lights fromthe elements of the ambient environment. To draw attention to thelights, their intensities are varied, usually either by flashing them orfocusing the lights into beams that rotate.

The visual effect of these flashing and/or rotating warning lights isgreatest when viewed from directly in front or behind the vehicle. Atintersections, however, the greatest danger of collision is derived fromapproaching vehicles in a crossing street or highway. These vehiclesview the row of warning lights on the emergency vehicle at angles up toapproximately 90° to the heading of the emergency vehicle. At suchangles, the profile of the lights is effectively narrowed, therebyreducing their visibility. Furthermore, the domes over the warninglights are often configured such that their transmittance at anglesapproaching 90° is significantly less than when the warning lights areviewed from directly in front of or behind the vehicle. The combinationof the reduced profile and transmittance seriously compromises thewarning ability of the lights for vehicles approaching the emergencyvehicle from a side angle, as is typically in an intersection.

SUMMARY OF THE INVENTION

It is a primary object of the invention to provide a light bar for anemergency vehicle having enhanced transmittance in directions at anangle to the heading of a vehicle carrying the light bar, whileproviding the same or better transmittance as conventional light barsalong the heading of the vehicle. In this connection, it is a moreparticular object of the invention to provide a light bar for anemergency vehicle having increased visibility as the vehicle enters anintersection.

It is another object of the invention to provide a light bar for anemergency vehicle that is able to directionalize its warning patterninto zones positioned about the vehicle.

It is a further object of the invention to provide a light bar for anemergency vehicle that has the foregoing characteristics and is easilyassembled and serviced. In this connection, it is a more particularobject of the invention to provide a modular design for such a lightbar.

It is a further object of the invention to provide a light bar that hasthe foregoing characteristics and is also aerodynamically efficient.

It is a further object of the invention to provide the foregoing lightbar with a stable mounting that does not require the drilling of holesin the roof of the vehicle.

Other objects and features of the present invention will become apparentto those skilled in the art upon reading the following detaileddescription and upon reference to the drawings.

In order to achieve the foregoing objects and others, the inventionprovides a light bar comprising a plurality of like signalling devicesdistributed on a frame that traverses a roof of a vehicle, where thesignalling devices are protected by a dome assembly that forms anon-linear pattern. The non-linear pattern of the dome assembly enhancesthe visibility of the warning pattern generated by the signallingdevices when viewed at an angle with respect to the heading of thevehicle carrying the light bar. Moreover, the non-linear patternfacilitates directionalizing the warning pattern into zones about thevehicle so that the visual effect of a warning pattern can be enhancedwhen viewed on one side of the vehicle with respect to the visual effectfrom the vehicle's other side.

Preferably, each of the signalling devices of the light bar is housed ina pod-like module mounted to the frame. The modules are similarly shapedand distributed along the frame to form a non-linear pattern when viewedfrom one end of the frame to the other. In the illustrated embodiment,the non-linear pattern is a V-shaped pattern. It will be appreciatedfrom the following detailed description, however, that other non-linearpatterns may also be implemented. The important factor in choosing anon-linear pattern is its ability to enhance the visibility of thewarning pattern at angles approaching 90° to the heading of the vehiclewhile maintaining the same or better visibility along the heading of thevehicle as is provided by conventional linear light bars.

Each of the modules comprises a base section for supporting one of thesignalling devices. A dome fits over the base and combines with it toisolate the signalling device from the elements of the ambientenvironment. Each of the domes surrounds the associated signallingdevice so that light emanating from the device is incident on the innersurface of the dome at an angle that remains close to 90 degrees. Bymaintaining such a relationship between the radiated light and the dome,the modules provide a high percentage transmittance of light in everydirection, thereby further enhancing the visibility of the warningpattern when viewed at an angle to the heading of the vehicle.

As an alternative to the modular construction of the preferredembodiment, the dome assembly for the signalling devices may extendalong the frame to cover more than one device. Although such aconstruction does not benefit as much from enhanced transmittance in alldirections as does a modular construction, it may nevertheless stillprovide enhanced transmittance at angles to the heading of the vehiclerelative to conventional linear light bars.

Preferably, each of the signalling devices comprises a reflector mountedto rotate about its focal point and a lamp positioned at the focalpoint. It will be appreciated, however, that many other types of visualsignalling devices can be substituted for the preferred one and theadvantages of the invention will still be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an emergency vehicle incorporating alight bar having a plurality of light modules mounted to a frame inaccordance with the invention;

FIG. 2 is a cross-sectional view of the light bar taken along the line2--2 of FIG. 1, showing a cross-sectional view of one of the lightmodules and the frame;

FIG. 3a is a schematic plan view of the light bar mounted on a vehicleillustrating the improved visibility provided by the light bar for anobserver positioned at an angle to the line of travel of the emergencyvehicle and also illustrating the ability of the light bar todirectionalize its warning pattern into zones;

FIG. 3b is a schematic plan view of the pattern formed by the modules,illustrating the ability of the modules to maintain a reasonably widedistribution of light even when viewed 90° from the heading of thevehicle;

FIG. 4a is an exemplary graph, using the Cartesian coordinate system,illustrating variable transmittance of light from a lamp through atransparent medium such as a dome of a light bar for different angles ofincidence, where the ordinate is the angle of incidence of the light indegrees and the abscissa is the amount of transmittance as a percentageof the incident light;

FIG. 4b is a schematic diagram illustrating the angles of incidence onthe dome of one of the modules for light radiating from a lamp withinthe dome;

FIG. 5a is an enlarged view of the cross-section of the light module inFIG. 2 more clearly illustrating the two major subassemblies of themodule--i.e., a base section and a dome;

FIG. 5b is an enlarged partial view of the light module in FIG. 5a,illustrating a tongue-and-slot assembly for securing the base section ofthe module to a front portion of the dome;

FIG. 5c is an enlarged partial view of the light module in FIG. 5a,illustrating a threaded screw assembly for securing the base section ofthe module to a back portion of the dome;

FIG. 6 is a plan view of the light module in FIG. 5a taken along theline 6--6;

FIG. 7 is a cross-sectional view of the light module in FIG. 6 takenalong the line 7--7;

FIG. 8 is a plan view of the light bar with all but one of the modulesremoved in order to more clearly illustrate the structure of the frame;

FIG. 9 is the same plan view of FIG. 8, except the cover for theelectronics of the light bar and the plates for mounting the moduleshave been removed in order to expose the basic framework and wiring;

FIG. 10 is a partial and enlarged view of the cross-sectional view inFIG. 2, showing a back end of the frame and its connection to a seriesof lights mounted to the end;

FIG. 11 is a side view of the light bar in FIG. 1 showing the mountingassembly for securing the light bar to the roof of the vehicle;

FIG. 12 is a partial perspective view of the underside of the light bar,with the components of the mounting assembly exploded in order toillustrate the composition of the assembly and its fastening to theframe of the light bar; and

FIG. 13 is a perspective view of a light bar according to an alternativeembodiment of the invention.

While the invention will be described in connection with a preferredembodiment and an alternative embodiment, there is no intention to limitit to those embodiments. On the contrary, the intent is to cover allalternatives, modifications, and equivalents falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning to the drawings and referring first to FIGS. 1 and 2, anemergency signalling system according to a preferred embodiment of theinvention is installed in an exemplary emergency vehicle 11 shown inbroken lines. The system 13 includes a plurality of like modules17(a)-17(g) housing signalling devices 20. The emergency signallingsystem 13 is mounted to a roof 19 of the vehicle 11, and the modules17(a)-17(g) are evenly distributed across the roof.

Emergency signalling systems of the type mounted to the roof ofemergency vehicles are commonly called "light bars" because they aretypically shaped as a linear bar that traverses the roof. In keepingwith this convention, the illustrated emergency signalling system ishereinafter referred to as a "light bar" since it is intended to bemounted to the roof of an emergency vehicle.

In the light bar 13, each of the signalling devices 20 is containedwithin one of the modules 17(a)-17(g). Each of the modules comprises abase section 12 and a dome 14 (as best see in FIG. 2) mounted to a frame16 that traverses the vehicle. The frame 16 supports a housing 15containing a portion of the circuitry for controlling the signallingdevices 20 as will be explained more fully hereinafter. The light bar 13is mounted to the vehicle 11 by way of a mounting assembly 18 at eachend of the frame 16.

Because each of the signalling devices within the modules 17(a)-17(g) isidentical to the other, a single reference number 20 will be used foreach of the devices, although separate devices are housed in each one ofthe modules. In the illustrated light bar 13, space in the housing 15 isreserved for a portion of the circuitry that controls each of thesignalling devices 20. The housing 15 is intended to provide an RFshield for the circuitry inside the light bar 13 since the vehicle 11will most likely be exposed to considerable RF noise. For example, thevehicle 11 is typically equipped with a two-way radio (not shown) whosetransmitter creates serious noise problems for the electronics in thelight bar 13 and, therefore, requires the electronics to be adequatelyshielded. Of course, the housing 15 must also protect electronics fromthe elements. Techniques for electrically and physically sealing thehousing 15 are well known in the art.

The frame 16 comprises two extruded members 21a-21b (see FIG. 9) thatare secured to one another to form a V-shaped base. Each of the members21a and 21b forms one wing of the V and meet at a vertex 23 formed bythe two wings of the V. The housing 15 for the circuitry controlling thesignalling devices 20 spans the members 21a and 21b and also provides abase for supporting a row of secondary lights 25 distributed across theback of the light bar.

Each of the extruded members 21a and 21b is of identical cross sectionand formed from aluminum by a conventional extrusion process to define achannel 27, best seen in FIG. 2, for communicating wiring emanating fromthe circuitry in the housing 15 to the signalling devices 20, each ofwhich comprises a lamp 29 and a stepper motor 31 mounted in the basesection 12 of each module 17(a)-17(g) for rotating a reflector 33. Forease of assembly and wiring of the light bar 13, the channel 27 opens atthe top of each member 21a and 21b. After the wiring has been placed inthe channel 27, a top plate 35 made of aluminum is received by a recessin the members 21a and 21b and secured by threaded screws 36 in order toclose the channel and isolate it from the elements of the ambientenvironment. The top plate 35 includes a variety of holes (see FIG. 8)for securing the modules 17(a)-17(g) to the frame 16 and forcommunicating wiring from the channel 27 to the signalling devices 20 asexplained more fully hereinafter.

In order to form the housing 15 and secure it to the extruded members21a and 21b, a bottom pan 37 is secured by threaded screws 38 to thebottom side of each extruded member 21a and 21b and extends rearwardlypast the member. The bottom pan 37 is made of aluminum and has thegeneral shape of a triangle in order to fit within the V-shape formed bythe two extruded member 21a and 21b. Circuit board assemblies 39a and39b are mounted on the bottom pan 37 and preferably provide programmablecircuitry (e.g., microprocessor-based circuitry) for controlling thestepper motor 31 and lamp 29 of each signalling device 20 in conjunctionwith additional circuitry (not shown) contained within the vehicle 11. Acontrol system that may be used in conjunction with the illustratedlight bar 13 is disclosed in co-pending Ser. No. 07/592,557 filed onOct. 4, 1990, assigned to the same assignee as that of the presentinvention. In this regard, any type of light radiating device (e.g., astrobe) may be substituted for the illustrated stepper motor 31 andincandescent lamp 29 since it is the relative positioning of thesignalling devices 20 rather than their composition that is important tothis invention. Nevertheless, applicants prefer the use of theillustrated stepper motor 31 for directly driving the rotation of thereflector 33 about its focal point. Because the stepper motor 31 movesin response to discrete pulses, it is particularly suitable for use withthe microprocessor-based control system disclosed in the aforementionedco-pending application.

In order to complete the housing 15 and isolate the circuitry 39a and39b contained within it from the elements of the ambient environment, atop pan 41 formed of aluminum is received by the extruded members 21aand 21b and the bottom pan 37. As best seen in FIG. 2, the top pan 41includes a flange 41a that is received by a mating slot in the extrudedmembers 21a and 21b in order to join the top pan to the members. Whenconsidered from the area of the flange 41a backward, the cross sectionof the housing 15 flares as best seen in FIG. 2. The flare provides asufficient vertical back portion 15a of the housing 15 for mounting therow of secondary lights 25 while minimizing the leading profile of thehousing so as to reduce wind resistance as much as possible.

In accordance with one important aspect of the invention, the signallingdevices 20 are distributed along the frame 16 to form a non-linearpattern that maintains a distributed light pattern when viewed at anglesto the heading of the vehicle 11 up to and including 90°, therebyenhancing the ability of the light bar 13 to attract attention whenviewed at severe angles to the heading of the vehicle. To facilitate themaintenance of the distributed light pattern at angles to the heading ofthe vehicle 11, the dome assembly for covering the signalling devices 20(e.g., the domes 14 of the modules in the illustrated embodiment) alsoforms a non-linear pattern that traverses the vehicle. Preferably, thenon-linear pattern formed by the dome assembly is the same as thatformed by the signalling devices. In the illustrated and preferredembodiment, the pattern is V-shaped. It will be appreciated by thoseskilled in the art of designing light bars for vehicles, however, thatother shapes may also be used for the non-linear pattern. For example,the pattern may be U-shaped or O-shaped. Some of the signalling devices20 could be aligned across the roof so that only a few create thenon-linear pattern. The important consideration in selecting a shape ofthe pattern is that it provides for a distribution of the signallingdevices 20 along the heading of the vehicle 11 so that a distributedlight pattern is seen when the vehicle is viewed from an angle.

In the illustrated and preferred embodiment, the dome assembly comprisesthe domes 14 of the plurality of modules 17(a)-17(g), where each domecovers only one signalling device 20. Asian alternative embodiment, thedome assembly may be a continuous canopy that covers more than one ofthe signalling devices 20. An example of such an alternative embodimentillustrated in FIG. 13, which is discussed in greater detailhereinafter.

Referring to FIG. 3a, the non-linear pattern of the illustrated lightbar 13 is symmetrical about a plane 43 that is orthogonal to the drawingand parallel to the heading of the vehicle 11. Each of the modules17(a)-17(g) and its associated signalling device 20 are offset in thedirection of the vehicle heading on either side of the plane 43 by adistance Z with respect to an adjacent module. In a direction traversingthe heading of the vehicle 11, each module 17(a)-17(g) is offset from anadjacent module by a distance Y. Because each of the offsets for one ofthe modules 17(a)-17(g) is substantially equal in magnitude to thesimilar offset of the other modules, the resulting pattern is theillustrated V-shape. If the offsets vary in magnitude, patterns of othershapes result. Preferably, the ones of the modules 17(a)-17(g) on eachside of the plane 43 define a wing of the V-shaped pattern whose angle θwith respect to the heading of the vehicle is approximately equal to45°.

Extending the wings formed by the modules 17(a)-17(g) on each side ofthe plane 43 by drawing a dashed line 45 and 47 past the end modules ineach wing as illustrated divides the area around the vehicle 11 intofour (4) quadrants or zones 1, 2, 3 and 4. By selectively operating thelamp 29 and reflector 33 of individual ones of the signalling devices20, the visual pattern collectively generated by the devices may bedirectionalized into any one of these four zones. For example, byoperating only the signalling devices 20 on the left-hand side of theplane, the visual pattern can be directed primarily into zone 4.Similarly, by operating only the signalling devices 20 on the right-handside of the plane, the visual pattern can be directed primarily intozone 3. Operating all of the signalling devices 20 distributes thevisual pattern among all four zones. By controlling the rotation of thereflectors 33, the visual pattern generated by the signalling devices 20can be directed into either zone 1 or zone 2 or simultaneously intozones 1 and 2.

An observer 49 positioned at an angle β with respect to the heading ofthe vehicle sees a distributed light pattern well beyond the angle 90°.As can be seen in FIG. 3a, the beams of light from the signallingdevices 20 remain visually discrete to the observer 49 who is viewingthe vehicle 11 at an angle β close to 90° from the heading. The greatestenhancement in the visibility of the visual pattern provided by thenon-linear shape of the light bar occurs at angles β greater than 45°.At an angle β of approximately 45°, an observer sees a distribution oflight that is approximately the same visual distribution offered by aconventional linear light bar. As the angle of the observer increasespast 45°, the distribution of light in a linear light bar quicklyshrinks and the beams blend and eventually are reduced to virtually asingle beam width at 90°. In contrast to this rapid reduction invisibility, the non-linear light bar of the invention maintains adistributed pattern of light beams well past an angle β equal to 90° asindicated by the projection of the light beams 50 onto a plane 52 inFIG. 3a. In essence, the non-linear light bar of the invention increasesthe visibility of the light patterns in zones 3 and 4 illustrated inFIG. 3a while maintaining the same degree of visibility provided byconventional linear light bars in zones 1 and 2.

Referring briefly to FIG. 3b, the distribution of light beams from themodules 17(a)-17(g) is viewed by an observer in the center of zone 1 toprovide a distribution of approximately the length l₁. As the observermoves away from the vehicle heading and toward zone 3, the distributiondecreases. At an angle β of 45°, the visual distribution is across alength l₂, which is equal to l₁ /√2. As the observer moves into zone 3and toward an angle β of 90°, the visual distribution decreases to alength l₃, which is equal to l₁ /2. By maintaining a substantialeffective distribution of the signalling devices at all angles of view,the light bar 13 is significantly more visible at angles approaching90°.

By providing the domed modules 17(a)-17(g) for every signalling device20 in the preferred embodiment, overall transmittance is enhanced atangles β to the heading of the vehicle 11, thereby further increasingthe visibility of the light pattern provided by the non-lineardistribution of the signalling devices. In conventional linear lightbars, the angle of incidence φ for a beam of light emanating from asignalling device 20 approaches 90° when the beam is viewed from theside of the vehicle. As indicated in FIG. 4a, the angle of incidence isconventionally measured from a reference that is perpendicular to theincident surface. As is well known, as the angle of incidence φincreases, the transmittance of light decreases. In the exemplary graphof FIG. 4a, it can be seen that the value of transmittance typicallystays quite high (e.g., 90%) until the angle φ exceeds some criticalangle X. At angles greater than the critical angle X, the transmittancequickly deteriorates until it reaches zero at an angle φ equal to 90°.

In a conventional linear light bar, at least some of the light beamsfrom the signalling devices 20 would be transmitted through the dome ofthe bar at angles greater than the critical angle X when viewed from theside of the vehicle 11. In contrast, the substantially teardropshapedmodules 17(a)-17(g) of the illustrated embodiment of the invention eachprovide a dome 14 surrounding and protecting one of the signallingdevices 20 such that the angle of incidence remains less than thecritical angle X for full rotations of the light beams formed by thedevices. Regarding the enhanced transmittance provided by the domes ofthe modules 17(a)-17(g), FIG. 4b illustrates in a schematic manner theangle of incidents for several beams of light emanating from one of thesignalling devices 20. For beams 51 and 53 directed along the heading ofthe vehicle 11, the angle of incidence φ is approximately 0°, thusmaximum transmittance is provided. As the beam sweeps through a 360°rotation in response to rotation of the reflector 33, the angle ofincidence varies as illustrated by the six beams 55-60. The three beams55-57 are the mirror images of the three beams 58-60 with respect to theplane of symmetry 61 of the dome 14 illustrated in FIG. 4b. The threeangles of incidents for the six beams are φ₁, φ₂ and φ₃ of which all areless than the critical angle X.

Referring now to the structure of the signalling devices and theirmodules 17(a)-17(g), FIGS. 5-7 illustrate the detailed construction ofan exemplary one of the signalling devices 20 in the module 17(d)illustrated in FIG. 2. As previously indicated, each of the signallingdevices 20 is identical to the others. Similarly, the modules17(a)-17(g) are identical except for differences in their shapenecessary to accommodate their mountings on different areas of the frame16. Therefore, only the signalling device 20 of the module 17(d) will bediscussed in detail hereinafter. As for the details of the constructionof the modules 17(a)-17(g), the following discussion refers to theillustration of module 17(d) in FIGS. 5-7, but applies equally to all ofthe other modules as well.

The stepper motor 31 directly drives the mounting 63 for the reflector33. In order to directly drive the reflector 33 and its mountingassembly 63, the motor 31 is mounted in a cavity 65 of the base section12 of the module 17(d) such that the drive shaft 66 of the motorprojects along a vertical axis through a hole 68 in the base section.

The mounting assembly 63 for the reflector 33 is fixed to the end of thedrive shaft 66 so that the assembly and reflector rotate with the shaft.The shaft 66 of the stepper motor 31 rotates in arcuate steps and,because the mounting assembly 63 and reflector 33 are secured to theshaft, they also rotate in arcuate steps. The mounting assembly 63extends horizontally in one direction to define an extension 63a thatinteracts with a position sensor 67 in order to provide a referencesignal to the microprocessor-based circuitry 39a-39b for the rotation ofthe reflector 33 about the lamp 29. For the reflector 33 to orbit thelamp 29 as the shaft 66 of the stepper motor 31 rotates, the reflectoris mounted to the mounting assembly 63 at a position that is offset fromthe vertical axis of rotation defined by the shaft. The amount of offsetdefines the radius of the orbit for the reflector 33 and positions thereflector so that its focal point is coincident with the position of thelamp 29. The direction and speed of the arcuate steps executed by thestepper motor 31, the mounting assembly 63 and the reflector 33 arecontrolled by a control system including the microprocessor-basedcircuitry 39a-39b in the housing 15 of the light bar.

The mounting assembly 63 for the reflector 33 is generally L-shaped asillustrated and formed from 0.040 inch thick C-1008 or C-1010 coldrolled steel. The reflector 33 is riveted to an upright arm 63b of themounting assembly 63 so that the reflector is offset from the axis ofrotation as previously mentioned. The reflector 33 is made of 3003aluminum and has a conventional surface contour of a paraboloid. Afinish is placed on the surface of the reflector 33 so that it has abeam of relatively intermediate width and sufficient candle intensity onand off the axis of the paraboloid such that both narrow and broad beamintensity requirements are met. To ensure sufficient beam width, thefinish of the reflector is prepared using a conventional chemicaldipping and anodizing process, commonly called "bright dipping." With asufficiently broad beam width and bright light source for the lamp 29,the signalling device is able to meet the photometric requirements(e.g., SAE requirements) for all the patterns commonly made by differenttypes of conventional rotators.

The lamp 29 is suspended above the axis of rotation for the reflector 33by a lamp mounting assembly 69. The assembly 69 includes a conventionallamp socket 71 for receiving a 50 watt single contact, bayonet base,halogen lamp, which is the preferred light source. A 50 watt halogenlight has sufficient intensity to satisfy on-axis photometricrequirements for any pattern the signalling device may be asked toexecute while complementing the beam width of the reflector 33 to alsomeet or exceed beam width photometric requirements for any pattern.Also, a 50 watt halogen lamp for each of the signalling devices 20 is apractical power level that can be supported by the electrical system ofthe vehicle 11, assuming that the number of signalling devices in alight bar is not excessive.

In each of the modules 17(a)-17(g) of the seven signalling devices 20, aplate 73 in the base section 12 provides structural support for mountingthe devices. The plate 73 in turn is secured to the base section 12 byfive (5) screws 75a-75e. The stepper motor 31 is mounted to theunderside of the plate 73 by two screws 77a and 77b and its shaftprojects through the hole 68 in the plate. As an aid in providingstructural support, the plate 73 is stamped to include raised ribs 79best seen in FIG. 6.

To support the lamp 29 and lamp socket 71 above and along the axis ofrotation and focal point of the reflector 33, the lamp mounting 69includes a one-piece frame comprising two legs 69a and 69b, eachsupporting a cantilevered arm 69c and 69d that is joined at its end tothe other arm. The joint formed by the mating of these two arms 69c and69d secures the lamp socket 71 over the axis of rotation. To provideadded structural strength, the arms include raised ribs 81. The mountingassembly 69 is formed from 0.059 inch thick 1008 or 1010 cold rolledsteel. The legs 69a and 69b are oriented so as to present a minimumprofile to the light radiating from the lamp 28. Each of the legs 69aand 69b includes a foot 69e and 69f, respectively, for securing themounting 69 to the plate 73 of the module. Each foot 69e and 69f issecured to the plate 73 by way of an expanding nylon fastener and screwcombination 83. The nylon fastener allows the assembly 69 to beelectrically common with the lamp socket 71 in that the fastenerselectrically insulate the assembly from the plate 73. As explained inconnection with FIG. 4, the lamp 29 is energized by grounding the socket71 and assembly 69.

The position sensor 67 is mounted to a tab 85 that is a vertically bentportion of the plate 73. Two screws hold the sensor 67 to a verticalface 85a of the bracket 85 so that the extension 63a of the reflectormounting 63 passes through a gap in the sensor 67 and breaks a lightbeam between a phototransistor and photodiode comprising the sensor.

Each of the modules 17(a)-17(g) of the light bar 13 includes the dome14, which is made of transparent plastic material such as lens gradepolycarbonate plastic. To form one of the modules 17(a)-17(g). the dome14 is secured to the front of the base section 12 by way of atongue-and-slot arrangement 87 as best seen in FIG. 5b and secured atthe back of the base by a pair of screws 89 as best seen in FIG. 5c.Tinnerman clips 91 cooperate with the screws 89 to fasten the dome 14 tothe base section 12 by way of a vertical extension 73a of the plate 73.With the domes 14 in place, the signalling devices 20 are isolated fromthe elements of the ambient environment. A gasket 93 is fitted between awall 12a of the base section and the rim 14a of the dome 14 in order toseal the junction between the two. Preferably, the gasket 93 need onlyextend about the front portion of each module since it is this areawhere high pressure caused by the movement of the vehicle 11 couldcreate a leak without the addition of the gasket. Under each of thedomes 14, a color filter 95 may be provided. These filters 95 fit intoslots formed by two pairs of opposing ribs 96 best seen in FIGS. 5a and6. The filters 95 are preferably each in front and tick sections so thatdifferent colors can be projected into different zones if desired.

A pair of cables 97a and 97b from the microprocessor-based circuitry39a-39b in the housing 15 of the light bar 13 feeds wires to the motor31 and lamp socket 71 of each signalling device 20 via the channel 27 inthe frame 16 as best seen in FIG. 8. Also, wires in one of the cables97a and 97b carry signals from the position sensors 67 back to themicroprocessor-based circuitry 39a-39b by way of the channel 27. A wire99 to the socket 71 for the lamp 29 is secured to one of the legs 69a or69b of the lamp mounting 69 and provides power to the positive terminalin the socket. In each of the modules, a connector 101 (FIGS. 5a and 8)mounted to the underside of the plate 73 interfaces the wiring of thesignalling device 20 and the wiring from the microprocessor-basedcircuitry 39a-39b.

As can be best seen in FIG. 8, the top plate 35, which is fitted into arecess of the extruded members 21a and 21b, is preferably comprised ofthree sections 35a, 35b and 35c. Each of the sections 35a-c includesports 103 for communicating the pair of the cables 97a and 97b from thechannel 27 of the extruded members 21a and 21b to the modules17(a)-17(g). One of the cables 97a and 97b includes a set of wires forcontrolling the motor 31, while the other cable controls the lamp 29 ofthe signalling device 20. In this regard, the module 17(g) isillustrated in FIG. 8 with its dome 14 removed in order to show thewiring from the port 103 into the signalling device 20. The portscommunicate into the interior of the modules 17(a)-17(g) by way of holesin the base section 12 and the plates 73 that align with the ports whenthe modules are mounted to the frame 16. Holes such as 105 illustratedin FIG. 8 are also provided in the three sections 35a-c of the plate 35in order to secure the base section 12 of each module 17(a)-17(g) to theframe 16. The extruded members 21a and 21b are capped at their end byface plates 107a and 107b.

Removing the top plate 35 and cover 41 of the housing 15 as shown inFIG. 9 exposes the recess 108 for receiving the plates 35 and therouting of the pairs of cables 97a and 97b for the seven (7) signallingdevices 20 of the illustrated embodiment. Cabling 109 from the controlsystem (not shown) for the light bar 13 communicates the control systemwith the microprocessor-based circuitry 39a-39b by way of a hole 110 inthe pan 37. Sub-circuit 39a includes seven ports 111, each providing oneof the cable 97a in the pair 97a and 97b going to one of the signallingdevices 20. Each cable 97a from the subcircuit 39a controls the motor 31of one of the signalling devices 20. Correspondingly, a sub-circuit 39bincludes seven ports 113, each port being associated with the othercable 97b in one of the pairs. Each cable 97b from the sub-circuit 39bcontrols the lamp 29 of one of the signalling devices 20. All of thecables 97a and 97b are communicated into the channel 27 provided by eachof the extruded members 21a and 21b by way of a gap 115 separating thetwo extruded members 21a and 21b. The gap 115 is tapered such that thetwo extruded members 21a and 21b meet at the vertex 23 of the taperedgap. A material made of closed cell neoprene rubber fills the taperedgap in the area beyond where the gap communicates to the channel 27.

A third sub-circuit 39c receives a portion of the cabling 109 from thecontrol system by way of a junction connector 117. The sub-circuit 39ccontrols the operation of the assembly of secondary lights 25 by way ofa pair of cables 119a and 119b that connect to a circuit board 121 foreach light contained within a housing 123 as best illustrated in FIGS. 2and 10. The pair of cables 119a-b from the sub-circuit 39c enter thehousing 123 by way of a hole (not shown) in the top pan 41 of thehousing 15. In order to secure the back of the top and bottom pans 41and 37 of the housing 15, the bottom pan includes a pair of brackets125a and 125b best seen in FIG. 9 taken in conjunction with FIG. 2. Thebrackets 125a and 125b are an extension of the aluminum that form thebottom pan 37. A spacer or standoff 126 is associated with each bracket125a and 125b in order to provide the flared cross section of thehousing 15 so that the back 15a of the housing has sufficient height forsupporting the secondary lights 25. The assembly of secondary light 25is attached to an L-shaped back portion 15a of the top cover 41 by wayof a plurality of threaded screws 127 as best seen in FIG. 10.

The row of secondary lights 25 is, in the illustrated embodiment, a rowof eight lamps 25a primarily intended for directing traffic approachingthe vehicle 11 from behind. The row has eight (8) individualpolycarbonate lens 129 and aluminum reflector sub-assemblies 131attached to a channel 133 formed by the housing 123, which is also madeof aluminum. Each lamp 25a, lens 129 and reflector assembly 131 form alight assembly that is secured to the housing 123 by two screws (notshown). The row arrangement of the secondary lights 25 allows them toflash in various patterns such as sequentially left to right or right toleft. By sequencing the lamps 25 from one end to the other, thesecondary lights 25 collectively function as an indicating arrow todirect vehicles to pass the emergency vehicle 11 on either its left orright side. An aluminum visor 135 surrounds the top and sides of thechannel 133 and the light assemblies. This visor 135 is secured in placeby mounting it between the top pan 41 of the housing 15 and the housing123 of the secondary lights 25. The printed circuit boards 121 hold inplace lamp sockets 137, and they snap into plastic standoffs 139 mountedinside the channel 133. A type GH22, bi-pin halogen lamps of 27 wattsare preferably used in each light.

As best shown in FIG. 12, two (2) carriage bolts 141a and 141b thatslide into the bottom of the extruded members 21a and 21b and protrudethrough a slot 143 in the bottom pan 37 of the housing 15 are used tosecure each of the two mounting assemblies 18 to the light bar. Each ofthe mounting assemblies 18 are mirror images of the other and,therefore, only one will be described in detail hereinafter.

Each of the assemblies 18 consists of a main mounting bracket 18a madeof cold-rolled steel. This bracket is configured so that the top of thebracket attaches to the carriage bolts 141a and 141b under the bottompan 37. The side of the bracket 18a has outriggers 18b and 18c forattaching two separate mounting foot brackets 143a and 143b, as well asan outrigger 18d to support a mounting hook 145. When each of themounting assemblies 18 is mounted to the light bar 13, the outrigger 18dis located approximately in line with the center of gravity of the lightbar 13. In order to make the mounting assemblies 18 adaptable to variouscontours and widths of roofs, the main mounting bracket 18a includes anextra screw hole 147. The outriggers 18b and 18c each receive pairs ofscrews 149 that secure the foot brackets 143a and 143b. The footbrackets 143a and 143b are also made of cold-rolled steel. A rubber pad151 snaps into the underside of each of the foot brackets 143a and 143band is used to protect the vehicle 11 from scratches and dents. Themounting hook 145 is made of cold-rolled steel and secures the light bar13 to the roof 19. One end of the hook 145 is secured under a raingutter 153 of the vehicle 11 (FIG. 12) and the other end is secured tothe outrigger 18d by way of a bolt 155 as best seen in FIG. 11.

The outrigger 18d and hook 145 are positioned to be in transversealignment across the roof 19 of the vehicle 11 with the center ofgravity of the light bar 13. Unlike conventional mounting assemblies forlight bars, however, the foot brackets 143a and 143b are not evenlyspaced from the outrigger 18d and hook 145 as can be best seen in FIG.11. The foot brackets 143a and 143b are separated by a distance D inorder to provide a sufficiently wide base for the mounting assembly 18to be stable. The moment arm 157 about the outrigger 18d and hook 145with reference to the forward foot bracket 143a is relatively shortcompared to the moment arm 159 about the outrigger and hook withreference to the rearward foot bracket 143b. The shorter moment arm 157aids in ensuring the hook and its connection to the outrigger 18d issufficiently strong to resist any rotational force resulting fromcurrents of high velocity wind passing the light bar 13. Strongrotational forces about the outrigger 18d and hook 145 are much lesslikely to be generated along the moment arm 159 of the rearward footbracket. Therefore, this bracket can be safely placed farther from theoutrigger 18d and hook 145 in order to ensure the mounting assembly 18has a sufficiently wide stance to be stable on the roof 19.

The mounting assemblies 18 at each end of the light bar 13 provide ahighly rigid mounting for the light bar. The rigidity of the light bar13 itself is aided by the housing 15 spanning the wings of the V-shapedframes 16. With a stable mounting and a rigid construction for the lightbar, applicants have found that a center support for the light bar 13 isnot necessary. Therefore, there is no need for holes to be drilled intothe center of the roof 19 or other type of modifications made to thevehicle 11 in order to support the light bar 13 on the roof. In order toensure the light bar 13 is leveled on the roof 11, the holes 160 inoutrigger 18c are elongated so the position of the foot bracket 143b canbe adjusted for the contours of different roofs. In contrast, the holes162 in the outrigger 18b are not elongated.

Finally, FIG. 13 illustrates an alternative embodiment of the inventionwherein a light bar 161 according to the invention includes a dome 163that forms a continuous closed canopy over the signalling devices (notshown) mounted to a V-shaped frame 165. As in the preferred toembodiment, a housing 167 contains microprocessor-based circuitry forcontrolling the signalling devices and a row of secondary lights 169mounted across the back of the housing 167.

The dome 163 may be formed of standard polycarbonate material and piecedtogether from two linear dome sections 163a and 163b that join at avertex 171 of the V-shape. The interior of each dome section 163a and163b provides a continuous cavity for mounting the signalling devices tothe frame 165. The signalling devices may be of any conventional type,or they may be the signalling devices 20 shown in the preferredembodiment.

The light bar 161 of FIG. 13 provides essentially the same enhancedvisibility when viewed at angles approaching 90° to the heading of thevehicle carrying the light bar as does the light bar 13 of the preferredembodiment. Because of the modular construction of the domes 14 of thelight bar 13, however, the percentage transmittance of light at anglesapproaching 90° may be slightly less for the light bar 161 than for thelight bar 13. Nevertheless, the light bar 161 still providessignificantly improved visibility at severe angles to the heading of avehicle relative to that provided by a conventional linear light bar.

From the foregoing, it will appreciated that the light bars 13 and 161provide enhanced visibility relative to conventional linear light barswhen viewed from an angle approaching 90° to the heading of the vehicles11 to which the light bars are mounted. In the light bar 13, the modules17(a)-17(g) for the signalling devices 20 provide high percentagetransmittance of light radiating from the signalling devices at severeangles to the heading of the vehicle 11. Furthermore, the non-lineardistribution of the signalling devices 20 allows for the devices to becontrolled in a manner that can directionalize the warning signalgenerated by the signalling devices into different zones surrounding thevehicle. These advantages over conventional non-linear light bars areachieved without sacrificing visibility of the light bar along theheading of the vehicle 11. By providing a housing 15, the light barincorporates programmable circuitry 39a-39b that advantageously utilizesthe versatility offered by the use of a stepper motor 31 to drive thereflector 33 in the preferred signalling devices 20. In this regard, theability of the light bar 13 to directionalize its warning signal is bestrealized by the signalling devices 20 driven by the programmablecircuitry 39a-39b.

We claim:
 1. A light bar for mounting to a roof of a vehicle andproviding a signalling pattern whose primary warning effect can bealternatively directionalized into at least four distinct zones aboutthe vehicle, the light bar comprising:a frame for traversing the roof ofthe vehicle; means at both ends of the frame for securing the frame toopposing edges of the roof; a plurality of signalling devices forradiating light distributed along the frame to form a non-linearpattern; and a dome assembly covering the signalling devices and mountedon the frame in such a manner that the assembly forms a non-linearpattern traversing the roof.
 2. A light bar as set forth in claim 1wherein the dome assembly comprises at least one continuous dome thatcontains two or more of the signalling devices.
 3. A light bar as setforth in claim 1 wherein the dome assembly comprises a plurality ofmodules, each module covering only one of the signalling devices.
 4. Alight bar as set forth in claim 3 wherein the dome assembly is shaped tosubstantially maintain maximum transmittance of light emanating from theplurality of signalling devices for light propagating at any angle to aheading of the vehicle.
 5. A light bar as set forth in claim 1 whereinthe non-linear patterns formed by the signalling devices and the domeassembly are substantially the same.
 6. A light bar as set forth inclaim 1 wherein the non-linear pattern formed by the dome assembly issymmetrical about a plane that is parallel to a heading of the vehiclewhen the light bar is mounted to the vehicle.
 7. A light bar as setforth in claim 6 wherein the non-linear pattern is approximatelyV-shaped.
 8. A light bar as set forth in claim 4 wherein each of themodules comprises a base section for supporting the signalling deviceson the frame and a transparent dome that provides a protective cover andmates with the base section in order for the module to surround andisolate the signalling device from the elements of the ambientenvironment.
 9. A light bar as set forth in claim 8 wherein thetransparent dome is secured to the base section for securing the dome tothe base section by a tongue-and-slot arrangement on one side of themodule and at least one threaded screw on the opposite side of themodule for completing the securing of the dome to the base section. 10.A light bar as set forth in claim 1 wherein the frame includes means forhousing microprocessor-based circuitry.
 11. A light bar as set forth inclaim 1 wherein the means for securing the frame to the roof includesfirst and second foot pads at each end of the frame for supporting theframe on the roof of the vehicle where a first axis passes through eachof the first foot pads and a second axis passes through each of thesecond foot pads such that a moment arm about one of the axes issignificantly greater than a moment arm about the other.
 12. A light baras set forth in claim 1 wherein the means for securing the frame on theroof of the vehicle includes means securing the frame to the roof onlyat the ends of the frame.
 13. A light bar as set forth in claim 1wherein at least one of the signalling devices includes a reflector anda lamp and means for rotating the reflector about the lamp such that thefocal point of the reflector is coincident with the position of the lampand the axis of the reflector's rotation.
 14. A light bar as set forthin claim 13 including a mounting assembly for each of the lampsassociated with the reflector wherein the mounting assembly includesmeans for supporting the lamp at the focal point of the reflector andsuspended above the means for rotating the reflector.
 15. A light bar asset forth in claim 14 wherein the means for supporting the lamp andsuspending it above the means for rotating the reflector is orientedwith respect to the lamp so as to present a minimum silhouette to thelight waves reflected by the reflector.
 16. A light bar for mounting toa roof of a vehicle comprising:a frame for traversing the roof of thevehicle; a plurality of signalling devices distributed along the frameto form a non-linear pattern that is symmetrical about a plane that isparallel to a heading of the vehicle when the light bar is mounted tothe roof; and an assembly providing a protective cover for each of thesignalling devices where at least one of the covers on each side of theplane . .are.!. .Iadd.is .Iaddend.offset in . .that.!. .Iadd.the.Iaddend.direction of the heading of the vehicle with respect to othercovers on the same side of the plane.
 17. A light bar as set forth inclaim 16 wherein the non-linear pattern is a particular pattern thatallows selective operation of the plurality of signalling devices todirectionalize the visual effect provided by the plurality of signallingdevices.
 18. A light bar as set forth in claim 16 wherein the covers area continuous dome on at least each side of the plane, which defines acontinuous interior space shared by all of the plurality of signallingdevices on the same side of the plane.
 19. A light bar as set forth inclaim 16 wherein the covers comprise a plurality of individual modules,with each module defining a confined interior space that contains andprotects one of the plurality of signalling devices.
 20. A light bar asset forth in claim 19 wherein each of the module includes a base sectionfor supporting the signalling device on the frame and a transparent domethat mates with the base section in order for the module to surround thesignalling device and isolate it.
 21. A light bar as set forth in claim20 wherein the transparent dome is secured to the base section by atongue-and-slot arrangement on one side of the module for securing thedome to the base section on one side of the module and at least onethreaded screw on the opposite side of the module for completing thesecuring of the dome to the base section.
 22. A light bar as set forthin claim 21 wherein each module includes means for mounting a colorfilter under the dome.
 23. A light bar as set forth in claim 16 whereinthe frame includes means for housing microprocessor-based circuitry. 24.A light bar as set forth in claim 16 including means at both ends of theframe for securing the frame to opposing edges of the roof.
 25. A lightbar as set forth in claim 24 wherein the means includes first and secondfoot pads for supporting the frame on the roof of the vehicle where thefirst foot pad is forward of the second foot pad when the light bar ismounted on the vehicle and the first foot pad is significantly closer toa transverse plane including the center of gravity of the light bar thanthe second foot pad.
 26. A light bar as set forth in claim 25 whereinthe means for supporting the frame on the roof of the vehicle includes apair of the first and second foot pads and each of the two first andsecond foot pads is positioned at the end of the frame so that the lightbar is supported on the roof only at its ends.
 27. A light bar as setforth in claim 16 wherein the pattern formed by the signalling devicesis V-shaped when viewed from above the bar and along the plane ofsymmetry.
 28. A light bar as set forth in claim 16 wherein the patternformed by the signalling devices is U-shaped when viewed from above thebar and along the plane of symmetry.
 29. A light bar as set forth inclaim 16 wherein the pattern formed by the signalling devices isO-shaped when viewed from above the bar and along the plane of symmetry.30. A light bar for mounting to a vehicle comprising in combination:acontinuous frame for traversing a roof of the vehicle; means at bothends of the frame for securing the frame to opposing edges of the roof;a plurality of signalling devices distributed substantially evenly alongthe frame to form a pattern that is symmetrical about a plane that isparallel to the heading of the vehicle when the light bar is mounted tothe roof such that each signalling device on one side of the plane isoffset relative to adjacent ones of the signalling devices in thedirection of the heading of the vehicle; a dome assembly for protectingthe signalling devices and transmitting light emanating from thesignalling devices where a portion of the assembly that transmits lightfrom one of the signalling devices in a direction transverse to theheading of the vehicle is offset in the transverse direction withrespect to the similar portions of the assembly for the other signallingdevices.
 31. A light bar as set forth in claim 30 wherein the domeassembly forms a continuous housing for the signalling devices on atleast one side of the plane.
 32. A light bar as set forth in claim 30wherein the dome assembly comprises a plurality of modules, each modulesurrounding one of the signalling devices and isolating it from theelements of the ambient environment.
 33. A light bar as set forth inclaim 32 wherein each of the modules includes a base section forsupporting the signalling device on the frame and a transparent domethat mates with the base section in order for the module to surround thesignalling device and isolate it.
 34. A light bar as set forth in claim33 wherein a tongue-and-slot arrangement secures the transparent dome tothe base section on one side of the module and at least one threadedscrew on the opposite side of the module completes the securing of thedome to the base section.
 35. A light bar as set forth in claim 34wherein each module includes means for mounting a color filter under thedome.
 36. A light bar as set forth in claim 30 wherein the base includesmeans for housing microprocessor-based circuitry.
 37. A light bar as setforth in claim 30 wherein the pattern formed by the signalling devicesis substantially V-shaped.
 38. A light bar as set forth in claim 37including a row of lights mounted to the frame and spanning the V-shapedpattern from both ends of the pattern and facing rearwardly with respectto the vehicle when mounted to it.
 39. A light bar as set forth in claim30 including a row of lights mounted to the frame spanning the patternof the lamps from both ends of the pattern and facing rearwardly withrespect to the vehicle when mounted to it.
 40. An emergency lightingsystem that includes a light bar for mounting to a roof of a vehicle ..and providing a signalling pattern whose primary warning effect can bealternatively directionalized into at least four distinct zones aboutthe vehicle.!., the system comprising: a frame for the light bar mountedto the roof of the vehicle; a plurality of signalling devices forradiating light distributed along the frame . .to form a non-linearpattern.!. .Iadd.substantially in a common horizontal plane; a mountingassembly for positioning each of the signalling devices relative toadjacent signalling devices mounted on the frame .Iaddend.such that ..more than.!. .Iadd.any .Iaddend.two .Iadd.or more .Iaddend.of thesignalling devices are distinctly visible . .in each zone and at allpositions within the zone.!. .Iadd.about the vehicle between a viewingposition coincident with a heading of the vehicle and a viewing positionapproaching a position perpendicular to the heading.Iaddend.; and asingle electrical control system for controlling the operation of eachof the plurality of signalling devices . .and for coordinating theoperation of each signalling device.!. in order to generate signallingpatterns employing some or all of the signalling devices.
 41. Anemergency lighting system as set forth in claim 40 including means atends of the frame for securing the frame to opposing edges of the roof.42. An emergency lighting system as set forth in claim 40 wherein eachof the plurality of signalling devices comprises:at least one lamp forradiating light; a reflector having a focal point for reflecting lightemanating from the lamp and collimating it into a beam; means forrotating the reflector about the focal point; a mounting assembly forthe lamp that positions the lamp at the focal point and suspends itabove the means for rotating the reflector; and the mounting assemblyincluding members that interrupt the beam of light from the reflector,but are positioned with respect to the beam to present a minimum profilein order to minimize the interruption.
 43. An emergency lighting systemas set forth in claim 40 wherein at least part of the single electricalcontrol system is contained within a housing incorporated into the lightbar.
 44. . .An.!. .Iadd.The .Iaddend.emergency lighting system as setforth in claim 40 wherein the .Iadd.distribution of the plurality ofsignalling devices is along the frame to form a .Iaddend.non-linearpattern . .is approximately V-shaped.!.. .Iadd.45. The emergencylighting system of claim 40 wherein the signalling devices aredistributed to form a V-shaped formation having a forwardly pointingvertex. .Iaddend..Iadd.46. The emergency lighting system of claims 40 or45 including a plurality of domes for covering the signalling devices,where each dome covers only one of the signalling devices..Iaddend..Iadd.47. The emergency lighting system of claim 40 wherein thesingle electrical control system includes programmable circuitrycontained within a housing that forms part of the light bar..Iaddend..Iadd.48. The emergency lighting system of claim 40 wherein atleast one of the signalling devices includes a sensor that provides asignal to the single electrical control system for resolving a positionof a light beam produced by the at least one signalling device..Iaddend..Iadd.49. The emergency lighting system of claim 40 wherein thesignalling patterns generated by the signalling devices are controlledby the single electrical control system to provide a primary warningeffect that can be alternatively directionalized into at least fourdistinct zones about the vehicle. .Iaddend..Iadd.50. A light bar formounting to a roof or a vehicle, the light bar comprising: a frame fortraversing the roof of the vehicle; means for securing the frame to theroof; a plurality of signalling devices for radiating light distributedalong the frame substantially in a common horizontal plane such as thatany two or more of the signalling devices are distinctly visible aboutthe vehicle between a viewing position coincident with a heading of thevehicle and a viewing position approaching a position perpendicular tothe heading; and a dome assembly covering the signalling devices andmounted on the frame in such a manner that the assembly forms anon-linear pattern traversing the roof. .Iaddend..Iadd.51. The light barof claim 50 wherein the signalling devices are distributed to form aV-shaped formation having a forwardly pointing vertex..Iaddend..Iadd.52. The light bar of claims 50 or 51 wherein the domeassembly covering the signalling devices includes at least one dome thatcovers only a single one of the signalling devices. .Iaddend..Iadd.53.The light bar of claim 50 including a single electrical control systemfor controlling the operation of each of the plurality of signallingdevices. .Iaddend..Iadd.54. The light bar of claim 53 wherein the singleelectrical control system includes programmable circuitry containedwithin a housing that forms part of the light bar. .Iaddend..Iadd.55.The light bar of claim 53 wherein at least one of the signalling devicesincludes a sensor that provides a signal to the single electricalcontrol system for resolving a position of a light beam produced by theat least one signalling light. .Iaddend.